Posted
by
timothy
on Wednesday February 09, 2005 @03:53PM
from the savaged-comes-later dept.

SeaDour writes "Earlier, it was reported that the data from a critical wind speed experiment onboard the Huygens probe to Titan was completely lost due to someone forgetting to turn on one of Cassini's communications channels. However, it now appears that ground-based radio telescopes from the National Radio Astronomy Observatory were able to record the transmission's many subtle doppler shifts and reconstruct that lost wind data. The winds altered the probe's horizontal rate of descent, thereby producing a change in the frequency of the signal received on Earth. Additionally, the resolution of the radio telescopes was good enough to track Huygen's position to within one kilometer, allowing for the creation of a three-dimensional model of Huygen's descent."

One of the backups, in this case, is the Robert C. Byrd Green Bank Telescope [nrao.edu]. I imagine that the telescope is located on Robert C. Byrd Highway, down the road from the Robert C. Byrd FBI Fingerprinting facility and just around the corner from the Robert C. Byrd Memorial High School.

Man, the Esteemed Senior Senator from West Virginia sure does a fine job of delivering the bacon...

It was descending at an angle due strong winds. It's rate of descent could be something like 2ft of horizontal movement for every foot of vertical movement (numbers made up on the spot). It's sometimes called a Glide Ratio.

Also, a brief look into the history of mathematics [tripod.com] will reveal a decimal system in use in India around 2100BC, the development of theories of a solar-centric solar system, and pi around 500 AD, and tangible proof of the development of zero and negative numbers around 650-ish AD (the 7th century, and yes, this is a huge accomplishment nit-wit). Additonally, the term sine is derived from an Indian word, as trigonometry o

Seriously, if you think about it, this makes perfect sense. The Earth is a rotating sphere, right? So unless an object approaching ground level happens to maintain a perfectly geosynchronous orbit around the Earth as it falls inward, it will hit the atmosphere at an angle and not straight down. So almost inevitably, there will be a horizontal component (think the base of the triangle where the trajectory/vector is the hypotenuse) to go with the vertical component. How much and in which direction(s) the object is deflected from its ordinary horizontal state (the result of the pure angle of entry into the atmosphere) gives direct indication about the presence, speed, and direction of any wind which might exist at that place. (Vertical deflection from standard gravitational acceleration gives important information about the stratification and density of the atmosphere in the same manner.)

The AC explained it better than I could (a picture is worth a thousand words). But, even if the probe came in straight on as it does in the top picture, it would still have a horizontal component. In that case, the horizontal component would be zero, or null.

Yeah. I mean, it's not like we should expect that a craft that had as many man hours go into building it and all of its components and launch systems as went into making the Linux kernel would have any bugs on its "first public release".:P

I find it kind of funny how people on slashdot, many of whom have jobs writing software, would have the nerve to insist on completely bugfree operation in the first real-world-test of a spacecraft. And while in the software world if a bug hits one of your customers yo

It was a bug in the series of sequences that were to run in order. Of the thousands of switch-togglings and other commands that needed to occur to make the mission a success, they missed one. Of course, the commands issued are just a small fraction of the total workload.

Programmers have no right to complain about errors like that. When you can write a program involving hundreds of thousands of man hours between all components that works 100% bug free (even little bugs - little bugs in space kill craft o

The original experiment using Cassini's onboard receivers would have had an accuracy of better than 1 m/sec and presumably similar positioning accuracy. Still, the probe accomplished a lot and was several different kinds of awesome.

It's one of those moments when you realize that you are living in a Star Trek episode. You know when something goes wrong and then one of the guys (I forget the names) goes like "Captain, I can compensate using *strange word* to modulate *strange word*...".

Whats strange about using a neutrino generator to modulate a tachyon field to create a holographic reconstruction ?

Nothing, until you route it through the deflector array to crate gravitic interference in the nearby protonic cloud that has been destabilizing the matter-antimatter interface preventing safe use of the main engines.

Back in middle school, my first "word" program was a qbasic "Random Star Trek Episode Generator" that worked exactly like that;) It normally tried to insert realistic sounding star trek technobabble - of course, I added in a few "funny" options it.

Worf: "Captain, we're experiencing a cheap plot device in Sector 6. It seems to be the work of underpaid script writers."

The Star Trek:TNG writer's manual called for you to use the word TECH every time you needed a word like that; they got their science advisor to fill it in later.

So you really would see scripts with "Captain, I can compensate using TECH to TECH..."

I can't help but think that the series would have been better if TECH hadn't been such a cop-out. Sci-fi is about people, not technology, but often it's about how people interact with technology. If you don't know anything about technology then it's just the way people interact with mumbo-jumbo.

Good writing is about people, but Sci-Fi is the setting... Some of us prefer people to be flying around in spaceships with things that go 'woosh' rather then on horses with pistols. That's why I don't watch westerns (which are also about people).

I don't think it is quite that amazing. Radio telescopes appear to have a good enough resolution to image details of radio sources in remote galaxies. Identifying the relative position of an active source in our solar system would seem to be a less complex problem.

NASA? you do realize Huygens was a ESA+NASA effort...and in fact, most of the probe's development was european? NASA's Cassini was the carrier of the probe, but the probe is an European accomplishment first.

oh puhlease... Must everyone always turn everything into a debate ? Okay, so what. congrats to ESA as well. My post was not about Nasa or esa or Uso or wtf... It's about people being persistent and believing in a solution and an outcome, no matter how big the problem may seem, and no matter how big the fuckup to work around.

It's almost as if the political climate on this forum supports the recognition of someone's feats only if they're considered an underdog?

You just have to find the underdog in the story and point them out, and the respect will flow. Humanize it a little.

It's not the USA that gets props, it's NASA (who's constantly fighting with the Guvm'nt for more funding). Or it's not NASA, it's the overworked and underpaid engineers who found a way to cobble something together out of shoestring and boot leather, push

It's almost as if the political climate on this forum supports the recognition of someone's feats only if they're considered an underdog?

That's not this forum, that's human nature. We naturally resent those in power, those with more money than us, etc. Why are movies always about the underdog winning, never about the current champion kicking ass? It's the same thing. Nietzsche called it the "Will to Power," and he makes an interesting case.

Well, smack my head and call me an idiot. I'd been under the impression that the Europeans were wholly responsible for this mission. Thanks to your comment, and a bit of googling, I now have a lot less respect for the European scientific community.

Sure, they built a dandy little lander, but frankly, how hard is it to design a vehicle that has to detach, decelerate, and deploy a parachute? NASA seems to have literally done the heavy lifting here. The Huygens probe was fairly small, compared to Cassini. NASA

So basically what they are saying is they should have used the space for some other experiment? The guy spending years setting up an experiment that never got turned on isn't as bad as designing a useless experiment taking up space on the probe. Or was the onboard experiment supposed to be much more accurate?

So basically what they are saying is they should have used the space for some other experiment?

Not really. Cassini would have received a stronger signal, and the changes in relative motion between Huygens and Cassini would have resulted in larger doppler shifts. This would have improved the precision and/or accuracy of the measurements. In addition one of the features of the DWE is the fact that the two oscilators were designed and calibrated to be extremely close to each other in frequency. Without

The receiver on the Cassini spacecraft didn't get turned on, but some very smart chaps here on Planet Earth listened very hard using some very expensive equipment and managed to hear the faint transmissions from Huygens anyway. Does that make more sense?

How about because there's no guarantee that we would have been able to reconstruct the data using land-based radio telescopes? You do recognize that this is an exceptional accomplishment that requires a lot more work (and most importantly, a lot more luck) than having the satellite record this data and send it back to us in digital, error-corrected form, right? Sure, there's no guarantee that we would have gotten the experiment either way, but the odds are a hell of a lot better.

Actually, it was. Guess which signal they measured the doppler shift of - it was the data signal for this very experiment. The issue was that Cassini forgot to relay it, so they had to rely on the weak signal from Huygens itself.

As someone else pointed out. The doppler data we got on Earth depended on the working ultra-stable oscilator [nasa.gov] on Huygens. However, there are some good reasons why it would have been nice for it's twin to be working on Cassini.

1: The two USOs were designed and calibrated to operate on the same frequency with a high degree of precision. The lack of a similarly calibrated USO on Earth adds a bit of error to the measurements.

2: Signal strength and doppler shifts measured by Cassini would have been l

Luck had nothing to do with it. The probe entering the atmosphere of a moon is a once in a lifetime opportunity for unique observation, much like the comet impact on Jupiter. Everybody that has the control to point a 'listening asset' would point it in that direction during that timeframe. It was a unique opportunity to get unique data. Everything else the radio telescopes listen to, will still be there the next day, the probe descent would not happen again.

They're quite old anyway, basically from the day after it landed. For example mentioned here [2020hindsight.org].Slashdot chose to post about the doomed mission [slashdot.org] instead, which made me believe it was indeed lost... but apparently it was like this all the time.

A lot of this work was done by the "Green Bank Telescope" aka the Great Big Telescope or GBT. You should check out [nrao.edu] the specs on this telescope. It is the world's largest fully steerable telescope and it is taller than the Statue of Liberty. I was a grad student while this was being built, and was always impressed when I saw presentations about the amount of work that went into creating this instrument. It is not nearly as famous as other telescopes like Hubble or Keck, but is very impressive nevertheless.

IIRC about half of the picures taken were relayed via the A channel and what we have seen is all B channel stuff only....Any chance of reconstructing those images from the ground-based recordings of the A channel, or is the signal so weak that all that can ever be deduced is the carrier frequency, not any data?

There was a long discussion about this on a prior slashdot story. My speculation is that because they appeared to use digital compression algorithms, recovery of the images is probably mostly a lo

Well then, good ol' Doppler made good for causing problems earlier during this mission problems (The signals from Huygens could not be received by Cassini due to Doppler shift, by getting Cassini into a different orbig (I presume more perpendicular to Huygens, this problem was overcome).

This might seem a little harsh, but why was a wind measuring experiment sent with the probe if we could gather the same data remotely via doppler shift measurements?

I imagine it's not the same data [or rather the same certainty or resolution], but still, wouldn't the space/weight be better spent on a different experiment if the wind study team could make do with the data gathered from doppler shift analysis?

No. What they're doing here is something that happened to have worked, but a) might not have, b) might have given corrupted data, and c) I believe would up giving less precise data (somebody mentioned 1KM of resolution rather than 1M.)

So, it's lucky for them that they managed to salvage something out of it, but it would have been far better and more useful to have had the experiment work properly and get the data they wanted.

This might seem a little harsh, but why was a wind measuring experiment sent with the probe if we could gather the same data remotely via doppler shift measurements?

They didn't gather all the data solely by measuring the doppler shift on a constant signal, if that's what you're thinking. The bulk of the data was collected wind measuring equipment and transmitted. The doppler shift of this data signal provided additional information. What they're saying is that they not only managed to recover the data sig

This hasn't gotten as much coverage, but a design oversight nearly cost all Huygens data. Doppler shift was not accounted for in the signal decode process. The mission plan had to be rewritten to find an alternative flight path that reduced the Doppler shift to within the limited acceptable tolerances. Fortunately, Cassini's approach to Saturn was accurate enough that enough fuel existed to allow this while preserving the latter part of the existing flight plan.

Of course, in retrospect, maybe earth-based monitoring would have come to the rescue in this event, in an even bigger fashion.

Did anyone watch the Daily Show where Jon Stewart was covering the Huygens probe and every time he said Huygens he said it like Professor Frink from the Simpsons? Huuuyyygens!!! Now whenever I see that word I immediately laugh:

Professor Frink teaching a kindergarten class, pushing one of those popcorn popper thingies with the colored balls inside:

Frink: "N'hey hey! Ahem, n'hey.... So the compression and expansion of the longitudinal waves cause the erratic oscillation -- you can see it there -- of th

Just to clarify, the "command" to turn "on" the oscillator for Channel A was not sent due to human error.
So that equates to no data sent to Earth from Cassini for that Channel which contains the wind data and half of the photos.
Channel B does not have a similar oscillator so it did not suffer from the same problem.

So my question is, what data did they get, (or could get potentially)?
Sounds like the photos will be lost because all they seem to have accomplished with the global radar conglomerate was a measurement of Huygens's Doppler shifting carrier wave signal.

This is probably not as accurate as the direct measurements but will give us a replay of the descent to within 1km thanks to some correlation to VLBI measurements taken on Earth also.

There is a heated debate between project teams going on in the background as to exactly where the probe landed.
So this data should do well to help pinpoint the location.

The second channel was not a redundant channel. Channel 1 was for the major data. Channel 2 was for half the total images uplinked to Cassini. Channel 2 was also dedicated to the Doppler data.Someone failed to turn on the receiver on the Cassini device. The data was transmitted on channel 2, just never received by Cassini.

Think it through, he isn't bitching about the slashdot moderation system, he's talking about _actual_ _karma_. The thing being saved is the mission (not some post).

See, that makes it a classic contextual justaposititon, which is at least a little amusing. I beginto think that we really do need the imaginary TNT service from those TV comercials. You know "is this funny?" "Yes, sir, you may laugh, but not that much..."/sigh...